Recently, in the portable information terminals, there have been ever increasing demands for inputting various documents, especially in the mobile computer environments. These documents vary in a wide range including A 4 size to those sizes wider than this. In an attempt to achieve these demands, conventional flat bed scanners have problems in which it is difficult to carry these and it is also impossible to input the paper face of a document having a large size. In order to solve these problems, for example, Japanese Patent Application Laid-Open No. 11-73494 has proposed the following method. In this method, a scanning process is carried out with the input apparatus made in contact with the document, and the document image is acquired as a plurality of partial images so that these are composed later to reproduce the document image. However, the action (operation) for carrying out the scanning with the apparatus made in contact with the paper face is inferior in operability, resulting in a problem of a long input time.
Recently digital cameras are utilized as portable type scanners. Such a technique has been disclosed by, for example, Japanese Patent Application Laid-Open No. 11-98485. In this method, an input apparatus is placed on the document side, and the input apparatus is allowed to pick up an image of the document, and a distortion due to the image pickup operation, in particular, in a diagonal direction is eliminated. However, problems with this image input apparatus disclosed by this Patent Publication are that the resolution in the input image tends to become insufficient as a whole and that the resolution tends to vary depending on portions thereof located in front the input apparatus and those portions located apart from the input apparatus.
Along with the development of digital image pickup apparatuses with high resolution, the number of pixels in a CCD image pickup element has been remarkably improved; however, these are still insufficient in picking up fine characters and patterns with good reproducibility. Therefore, a process has been proposed in which each portion of an image pickup subject is picked up as a partial image, and these partial images are composed so that an image that looks as if it were taken by using an image pickup element having pixels with high density, with a wide angle. When an image with high precision is generated by using this composing technique of these partial images, the following points need to be taken into consideration.
More specifically, each of the partial images requires an overlapping area with respect to the adjacent partial image. The composing process for the respective partial images is carried out based upon image information on this overlapping area. In general, the greater the overlapping area, the higher the precision in the image composing process. However, on the other hand, there is an increase in the number of partial images to be picked up, and consequently, an increased processing time in the image composing process.
In this manner, when these partial images are picked up, it is necessary to pick up images so as to maintain overlapping areas with a proper number of images. However, such an operation imposes considerable skills and errors on the photographer's side. In order to solve these problems, for example, Japanese Patent Application Laid-Open No. 7-107379 has proposed “a still image pickup apparatus”. In Figures, reference number 1 represents an image pickup section for picking up an image from each portion of an image pickup subject, and for successively outputting the resulting image data, reference number 2 represents a pickup position orientation measuring section for measuring the position and orientation of the image pickup section 1, and for outputting position orientation information, reference number 3 represents an image selection section for finding the range of each image to be picked up on the image pickup subject based upon the image data and the image pickup range information successively sent from the image pickup section 1 as well as based upon the position orientation information sent from the pickup position orientation measuring section 2, and reference number 4 is an inner memory in which image previously picked up are stored.
In this still image pickup apparatus, the input apparatus is held by the hand on a document, and the image pickup face is mechanically shifted so that, at each position, each partial image is automatically picked up by the image pickup face in a manner so as to have overlapping areas. However, it is not possible to input the paper face of large size paper, and it is necessary to take into consideration influences from the hand shaking, with the result that the overlapping areas are taken in an excessive manner.
Japanese Patent Application Laid-Open No. 9-261520 discloses an image input apparatus which can pick up a partial image with a proper amount of overlap being maintained, while a scanning process is carried out over a document by the hand in a non contact manner. As illustrated in FIG. 20, in this arrangement, the position orientation of the input apparatus (pickup section 1) is measured, and based upon measuring information related to the position orientation, the current image pickup range on the document is calculated, and based upon the results of the calculations, the amount of overlap over the previously picked up image is estimated so that it is possible to carry out an image acquiring operation at the time when an appropriate amount of overlap has been obtained during the scanning process. Moreover, in this case, the size of the overlapping area is determined depending on the pattern matching (mutual correlation) between the two images in the input images.
However, the problem with the above mentioned conventional image input apparatus as described in Japanese Patent Application Laid-Open No. 9-261520 is that the orientation angles and positions of the input apparatus with 6 degrees of freedom with respect to a subject need to be detected, with the result that the apparatus becomes bulky and expensive in order to carry out these detections, resulting in an expensive apparatus; therefore, this method is not suitable for a practical use.
Moreover, the size of the overlapping area is determined by using pattern matching from an input image; however, in order to achieve this process, it is necessary to input image at high speeds, with the result that a very expensive image pickup element is required and the apparatus is limited in the usable environments.